St. Optatus on Schismatic Brethren

Lest any one should say, that without thought I call them brethren, I would reply that such they are, for we cannot escape from the words of the prophet Isaiah; and, although they would not deny (as all men know well) that they hold us in abhorrence, and ban us utterly and are unwilling to be called our brethren, still we may not depart from the fear of God, for the Holy Spirit exhorts us by Isaiah the prophet, saying:

‘You who fear the Word of the Lord, hear ye the Word of the Lord. ‘To those who detest and curse you, and are unwilling to be called your brethren, say ye nevertheless: “You are our brethren.” ‘ (Isa. 66:5 LXX)

They therefore are without doubt brothers, though not good brothers. Wherefore let no one marvel that I term those brothers, who are unable to escape being our brethren. They and we have one spiritual birth, though widely differing is our conduct. For even Ham, who mocked undutifully at his father’s shame, was the brother of the innocent. In accordance with his deserts, he incurred the yoke of slavery, so that he — their brother — was assigned in bondage to his brethren. From this we see that, even where there is sin, the name of brotherhood is not lost. Concerning the sins of these our brethren, I will speak in another place. For they, sitting over against us, speak evil things about us. They consort with that Thief who robs God, and share their lot with adulterers (that is, with heretics), and make their sins an object of praise, and plan reproachful words against us Catholics. (Against the Donatists Book the First III)